Homalium glandulosum Tagane & V. H. Nguyen, 2016

Tagane, Shuichiro, Nguyen, Viet Hung, Ngoc, Nguyen Van, Son, Hoang Thanh, Toyama, Hironori, Yang, Chen-Jui & Yahara, Tetsukazu, 2016, Homalium glandulosum (Salicaceae), a new species from Vu Quang National Park, North Central Vietnam, PhytoKeys 58, pp. 97-104 : 99-100

Homalium glandulosum Tagane & V. H. Nguyen sp. nov. Figures 2 , 3

Diagnosis.

Similar to Homalium petelotii Merr., but differing in having distinct glands, often stalked, at base of lamina and along margin of stipules and bracteoles, and spreading hairs on rachis of inflorescences, calyx tubes, sepals and petals (vs. glabrescent or only short appressed hairs in Homalium petelotii ). Also, similar to Homalium cochinchinense (Lour.) Druce and Homalium mollissimum Merr. but distinguished from these two by the distinct glands mentioned above and very sparsely pubescent branches and petioles (vs. pubescent to densely pubescent).

Type.

VIETNAM. Ha Tinh Province; Vu Quang National Park; along the trail to the summit; in hill forest, alt. 453 m, 18°16'25.3"N, 105°21'40.8"E, 25 July 2015, Tagane S., Yahara T., Toyama H., Nguyen N., Yang C. J. & Nguyen H. V3735 (holotype KYO!; isotypes BKF!, DLU!, FU!, NTU!, the herbarium of Vu Quang National Park!).

Description.

Small tree, 9 m tall, DBH 15.6 cm; bark gray-brown; branchlets very sparsely pubescent, soon glabrous, with many lenticels, which are narrow to broadly elliptic, 0.3-0.9 × 0.1-0.25 mm, whitish; young twigs blackish when dry, old twigs grey-brown. Leaves: simple, alternate, petiole 2.5-5 mm long, sparsely pubescent when young, blackish when dry; leaf blade ovate to elliptic-ovate or oblong-ovate, (2.4-)3.5-9.8 × (1.0-)1.2-3.1 cm, papery, very sparsely pubescent on both surfaces, apex acuminate to acute, rarely obtuse, with a gland on tip, base cuneate, with 2-5 pairs of stalked glands at border with petiole, margin crenulate with glandular teeth; midribs prominent on both surfaces, glabrescent, secondary veins 6-7 pairs, arising at an angle of 40-45 degrees from the midrib, slightly prominent on both surfaces, tertiary veins reticulated, visible when dry. Stipules narrowly triangular, ca. 5 × 1 mm, thinly papery, with 4-6 glandular teeth per side, glands often stalked, apex acute, with a gland on tip, blackish when dry, very sparsely pubescent, caducous. Inflorescences axillary, pendant, racemes or racemiform panicles with flowers borne singly on rachis or in clusters of up to 3 sometimes on short branches, 4-9 cm long, 7-20 flowered; rachis densely pubescent with spreading hairs except glabrous and lenticellate basally; bracts caducous, not seen. Pedicels 2.5-3.5 mm long, densely pubescent with spreading hairs; bracteoles narrowly ovate, 2.5-3 mm long, margin with 3-5 stalked glands per side, glabrous except near base, caducous. Flowers fragrant, 6-8 mm in diam.; calyx tube ca. 2.5 mm long, densely pubescent with spreading hairs; sepals 8, narrowly oblanceolate, ca. 3 × 0.5 mm long, membranous, with conspicuous midvein, light green in vivo, glabrescent except near basal part on both surfaces and ciliate margin, hairs spreading, 0.6 mm long, apex apiculate, with a gland on tip; petals 8, oblanceolate, 3.5 × 1.1 mm, membranous, with conspicuous midvein and lateral veins, whitish in vivo, glabrescent except lower 1/3 on both surfaces, margin ciliate with spreading hairs, hairs ca. 0.6 mm long, apex obtuse to acute. Disk glands 8, ca. 0.3 mm in diam., orange in vivo, black when dry, stipitate, stalk ca. 0.15 mm long, sparsely hairy. Stamens 8, filaments ca. 5.5 mm long, sparsely spreading hairy in lower 3/5; anthers ca. 0.4 mm long, longitudinally and extrorsely dehiscent. Ovary semi-inferior. Styles 3 or 4, filiform, ca. 5 mm long, united in lower 1/3, hairy in lower 1/2, hairs spreading; placentas 3 or 4, each with (3-)4 ovules, sparsely hairy inside. Fruits not seen.

Distribution.

So far known only from the type locality.

Habitat and Ecology.

Rare in hill evergreen forest, at alt. 453 m. Flowering specimens were collected in July.

GenBank accession no.

Tagane et al. V3735: LC0901208 (rbcL), LC0901207 (matK). The BLAST similarity search based on the matK sequence of Homalium glandulosum resulted in homology as high as 834/835, 773/774, 767/768 bp with the sequence of Homalium cochinchinense (GenBank accession no. HQ415362, KP093841, KP093840, respectively) in the DNA database.

Etymology.

The specific epithet ' glandulosum ' reflects the existence of distinct glands, often stalked, on stipule, leaf base and bracts.

Conservation status.

Data Deficient. Only one flowering individual was found in a protected area of Vu Quang National Park. Further efforts for finding additional individuals/populations are needed to evaluate its conservation status.

Note.

In Vu Quang National Park, another species of Homalium , Homalium cochinchinense , occurs in lowland forest (e.g., alt. 70 m, 27 July 2015, Tagane et al. V3818 (BKF!, DLU!, FU!, NTU!, the herbarium of Vu Quang National Park!). The species is easily distinguished as in the above diagnosis and the following key.

Figures

Figure 2. Homalium glandulosum Tagane & V. H. Nguyen: A habit B a flowering branch C abaxial leaf surface D bark E apical branch showing glandular stipules and leaf base F inflorescence G close up view of flowers.

Figure 3. Homalium glandulosum Tagane & V. H. Nguyen: A flowering branch B stipule and base of a leaf C bracteole D flower E longitudinal section of gynoecium.